Method of fabricating a composite steel article

ABSTRACT

A composite alloy article and method for producing the same wherein the article, which may be cylindrical, has an alloy core surrounded by compacted alloy powder; the core is preferably relatively tougher and more machinable than the alloy powder. The composite is produced by isostatic compacting at elevated temperature. Preferred articles would be cutting tools, such as hobs and milling cutters.

Unlted States Patent 1 1 [111 3,803,702 Bratt et 1. 1451 Apr. 16, 1974 1ME'rlitmoF FABRICATING A COMPOSITE 3.109.224 11/1963 Fearnside 29/4205 xSTEEL ARTICLE 3,279,917 10/1966 Ballard et a1. 29/D1G. 31 3,678,567 71972 Manilla et 211.... 29/4205 Inventors: Rlchard Bra", Syracuse,3.753.704 8/1973 Manilla et a1. 75/208 R Gary Steven, Mount LebanonTownship Allegheny County Pa FOREIGN PATENTS OR APPLICATIONS 587,8 7 5947 0 1a 29 420.5 [73] Assignee: Crucible Inc., Pittsburgh, Pa. 2 IIfeat mam [22] Filed: June 27, 1972 Primary Examiner-Charles W. LanhamAssistant Examiner-D. C. Reiley, Ill

[57] ABSTRACT [52] US. 29/4205, 29/D1G. 31, 75/208 R,

75/226 A composlte alloy artlcle and method for produclng 51 1m. (:1112213/24 the Same wherein the icle, hich may be cylindri- 5 1 Field fSearch H 29/1316. 31 4 4205, cal, has an alloy core surrounded bycompacted alloy 29/1912, 821; 75/208 R, 226 powder; the core ispreferably relatively tougher and more machinable than the alloy powder.The compos- [56] References Cited ite is produced by isostaticcompacting at elevated UNITFD QTATES PATENTQ temperature. Preferredarticles would be cutting tools,

such as hobs and milling cutters. 2,938.79] 5/1961) Blainey 75/2262.992.172 7/1961 Blniney et a1. 75/208 R 9 Claims, 4 Drawing Figures r)QL /0 H) 1.!

.1", u l ,Lif/ r 1'! I) f l ;r) Pitta/l2 p 1\ I k I J {J1 1 I 1 1 re/"/6 I I a Y "I V 55 I"? PATENTEH APR 15 IQF FIG F/GZ

FIG. 3

FIG.

COMPAC TED POWDER CORE METHOD ()F FABRICATING A COMPOSITE STEEL ARTICLEIn many final-product applications wherein powder metallurgy techniquesare used in production, it is desirable to have articles characterizedby a hard, wear resistant exterior and a relatively tougher and moremachinable interior. For example, it is known to produce hobs by powdermetallurgy techniques. In this application a charge of high-speed steelpowder is compacted at elevated temperature to form a cylindercorresponding generally to the desired size of the hob. After for mationof the compacted cylinder it is necessary to drill an axial boretherethrough and also to provide a keyway within the bore, all for thepurpose of accommodating the shaft of the hob. This operation isdifficult because the material that must be drilled and machined ishigh-spccd steel, which of necessity must be used in the manufacture ofthe hob to provide the required cutting ability and wear resistanceduring use. Therefore, it would be desirable to have an article thatwould provide the desired hardness and wear resistance where requiredfor cutting use and yet be readily machinable to permit the requiredmachining and drilling.

in addition there are products that are made by powder metallurgytechniques wherein teeth or other irregular cutting surfaces areprovided in the extremely hard surface of the article. To prolong thelife of such products, particularly by preventing breaking off ofcutting teeth and the like at the root, it would be desirable if theroot were of relatively tougher material than that of the remainder ofthe teeth.

It isaccordingly a primary object of the present invention to provide acomposite article, preferably for cutting applications and a method ofmanufacturing the same by powder metallurgy techniques, whereincompacted powder surrounds and is metallurgically bonded to a core ofrelatively tougher and more machinablc alloy so that the compactedpowder defining the exterior of the article Provides the desired cuttingability and wear resistance, and the core provides the requiredtoughness and machinability.

These and other objects of the invention as well as a completeunderstanding thereof may be obtained from the following description,specific examples and drawings, in which:

FIG. 1 is a schematic showing in vertical cross section of an assemblyin accordance with the present invention for compacting in accordancewith the method of the present invention to produce the compositearticle of the invention;

FIG. 2 is a schematic showing of the assembly of FIG. 1 aftercompacting;

FlG. 3 is a transverse cross section through a composite article inaccordance with the present invention; and

PK]. 4 is a photomicrograph (magnification lOOOX) showingthemetallurgical bond achieved in the article of HO. 3.

Broadly the method ofthe present invention is for the production of acomposite alloy article consisting of an alloy core surrounded bycompacted alloy powdenThe article is produced by surrounding a fullydense alloy core with alloy powder to form an assembly and isostaticallycompacting the assembly at a temperature sufficient to compact thepowder to a density greater than 95 percent of theoretical andmctallurgically bond the same to the core to form a composite article.After compacting, if it is desired to further decrease at dimension ofthe article, it may be mechanically worked, typically at conventionalhot-working temperatures on the order of l,700 to 2,200 F. In the caseof composites wherein the powder consists of a high-speed alloy suchtypically would be isostatically compacted while at a temperature. onthe order of 2,000 to 2,300 F. Compacting pressures of l0,000 to 20,000psi could be employed. it is necessary to achieve compacting by the useof isostatic pressure so that the required high densities andmetallurgical bond may be produced, while maintaining the productuniform throughout. For this purpose, various pressure vessels orautoclaves employing a fluid pressure medium, such as nitrogen orhelium, may be used; although various apparatus of this type aresufficient for use in the practice of the invention, one example thereofis that shown in Boyer U.S. Pat. No. 3,543,345.

In applications such as the manufacture of hobs wherein provision mustbe made for an axial bore to accommodate a shaft, the alloy used for thecore of the composite hob is relatively tougher and more machinable thanthe alloy of the powder, which must be hard and wear resistant for usein cutting. In this manner the relatively more machinable core may bedrilled to provide the bore necessary to accommodate the shaft. Thenecessary key-ways for securing the shaft may be easily provided byconventional machining operations. The exterior constituting thecompacted powder then constitutes the surface in which the cutting teethare pro vided. 1n applications involving the manufacture of hobs, tofacilitate machining the key-ways and to provide a tough ductile sleeveabout the shaft, it is preferred that a concentric margin portion of thecore be left surrounding the bore during the drilling operation. It ispreferred for the purpose of hob manufacture that the composite comprisea low-alloy steel core and a high-speed steel in powder form compactedaround and mctallurgically bonded to the core.

For manufacture of this composite hob the core and powder would beplaced in a container, which would typically be constructed of mildsteel, to form an assembly; the container would be evacuated and sealedagainst the atmosphere, the assembly heated to an elevated temperatureand then compacted in the autoclave while at elevated temperature. Bythe use of isostatic compacting and compacting temperatures on the orderof 2,000 to 2,300 F, it is possible to consistently achieve densities ofpercent and greater of theoretical, which are necessary to insureproduct integrity, particularly for high-speed cutting applications.

For purposes of this invention the term low-alloy steel" is defined as asteel consisting of 0.15 to 0.70 percent carbon, plus alloying elementswhich might include up to 2 percent manganese, up to 0.50 percentsulfur, up to 2 percent silicon, up to 4 percent nickel, up to 6 percentchromium, up to 2 percent vanadium, up to 2 percent tungsten, up to 2percent molybdenum, and the balance iron; it is understood that withinthe limits of this definition of low-alloy steel there may becompositions that would typically be regarded in the art as carbonsteels as well as medium-alloy steels. The term high-speed steel isdefined as a steel consisting, in weight percent, of 0.80 to 3.00carbon, up to 2 manganese, up to 1 silicon, up to 0.5 sulfur, up to 18tungsten, up to 10 chromium, up to l2 molybdenum, up to 3 5 vanadium, upto l2 cobalt and the balance iron, with tungsten -l molybdenum chromiumvanadium being equal to at least percent.

For manufacture of cutting tools, which is the pre 16. A thin-walledtube section is positioned axially with respect to bar [6 and extendsfrom the end thereof to the top of container 12 and surrounds the stem14. The tubing section 20 may be of any material that is ferredapplication of the invention, the composition se- 5 readily collapsibleand more specifically of a material lected for the core material will bebased on the followand construction that will collapse and compact alonging: with the container 12 and powder 18 upon application 1. low costrelative to the cutting-material portion of of isostatic pressure.During the pumping of the conthe tainer interior incident to outgassingthe tubing section 2. fCillIllly lilltClllIlZlblC pl'lOf IO hardening OitlTC artil0 prcvcnts any ubstantial quantity of the powder from beingremoved from the container or otherwise 3. compatible with the heattreatment required for b t ti ll di b d the hardening ofthecutting-material portion of the Th e bly 10, as hown in FIG, 1, isheated to a and compacting temperature on the order of 2,000 to 4.sufficient strength and toughness to withstand ini- I5 2300" F t il by li the same in a furnace tial shock and continued torque during cutting.(not shown), and when heated to this temperature the To achieve acomposite article wherein the powder assembly is placed in an autoclave(not shown) for is compacted to uniform density it is preferred in thecompacting in the well-known manner by the applicapractiee of theinvention to terminate the core short of 'tio ffl id re s re. Generallynitrogen or helium gas the end of the container to provide a void spaceand fill 20 is used as the pressure media. Upon compacting the top thecontainer with powder to a level not less than the f th nt in 12 illcollgpsc if l i h h btermination of the core. Then the remainingportion, or ing section 20 to provide a true isostatic condition withvoid space. of the container is provided with a material respect to theassembly 10, as shown in H6. 2, to result that will maintain the powderin place prior to comin a fully dense, homogeneous product. pacting, andparticularly during outgassing, and col- [t is understood that tubing 20may be replaced by lapse along with the container and powder during theany material that will readily collapse along with the application ofisostatic pressure for compacting. In this container 12 and thus providefor uniform pressure apmanner the pressure exerted along the top of theasplication and uniform compacting along the top of the sembly is equalto that exerted about. the sides and such assembly 10 while preventingsubstantial removal or results in uniform density. The material used forthis disturbance of the powder prior to compacting. purpose may beadditional powder a thin-walled tub- A composite alloy article resultingfrom the method ing in axial alignment with the core, steel wool or a ofthe invention as described above may be seen in con-ibination of thesematerials. cross section in FIG. 3, prior to removal of the conin usingthe invention for the manufacture of hobs, tainer. This FlGURE shows, intransverse cross section. the preferred final product would comprise acylindria cylindrical article consisting of a cylindrical bar as an calcomposite article having an axial drilling to accomaxial core with alloypowder compacted therearound to modate a shaft with the bore surroundedby a sleeve of substantially 100 percent density; the aritcle issurlow-alloy steel in which the required key-ways are maounded by thontainer, whi h is removed as by a machined; metallurgically bonded tothe sleeve is comehining operation. The compacted powder, as may bepacted high-speed steel powder of a density greater seen in FIG. 4, ismetallurgically bonded to the core by than 95 percent of theoretical andinto the exterior of the combination of high temperature and isostaticpreswhich is formed an irregular cutting surface. sure.

With reference to the drawings, and for the present If the compositearticle is to be used in the manufacto FlGS. 1 and 2 thereof. there isshown, in accordance ture of a hob an axial drilling would be madethrough with the present invention, an assembly designated genthearticle at the core. Customarily a margin or sleeve erally as 10including a mild steel cylindrical container of the core material wouldbe left around the bore dur- 12 ith a m 14 for Connection to p p ing thedrilling operation to provide for machining of shown) for evacuating theinterior of the container innecessary key-ways and also to provide atough. crackcident to outgassing in accordance with conventional i mm bhi th t wo ld id th de ir d ra k p d m a y practice- The Stem v gresistance under the torque resulting from rotation of sing has beencompleted, may be closed to seal the conth h ft lu in utti a li ationtainer 12 against the atmosphere prior to heating and Alternately aftercompacting ifit is desired to reduce compacting. The assembly furtherincludes a solid cyf rth r th di ension of the om osite article suchlindrical bar 16, which may be of low-alloy steel, axially maybereheated to a satisfactory hot-working tempcra-' positioned within thecontainer 12 and having an upper t r d th ti l m b hot wo k d i th wllend. as viewed in the drawings. terminating a distance kno n onve tioal m n r. from the upper end of the container 12. The container As aspecific example of the practice of the invention 12 is filled withalloy powder 18, which may be hightwo compacts in accordance with thepresent invention speed steel, to a level not less than the upper end ofbar were produced using the alloys listed in Table l:

TABLE I Composition (wt 9? Alloy C Mn Si Cr V W Mo S Fe REX M7 L00 0.300.30 3.75 2.00 1.75 8.75 0.025 max. Bill. RFX MES H(. L00 .30 .30 4.15 L6.40 5.00 .l5 Bal. (SM 0.30 .30 .50 1.65 0.43 .025 max. Bfll. MAXEL 3'.50 [.25 0.65 .13 .08 Bal.

EXAMPLE I A cylindricalmildsteel containeriii in. long and having anoutside diameter of in. and an inside diameter of 9% in. was providedwith an axial, cylindrical core of the CSM 2 composition set forth inTable l; the core constituted a rod 42 in. long with a 3% in. diameter.The. container was then filled with powder of the REX M7 compositionlisted in Table l to a height in the container substantiallycorresponding to the end of the rod. The void remaining in the upper endof the containerabovc the end of the rod and the powder level was filledwith steel wool. The container was outgassed to remove any moisturetherein, sealed against the atmosphere and then transferred to a furnacewherein it was heated to a temperature of about 2,200 F. It was thentransferred to an autoclave where it was compacted to a densityapproaching 100 percent of theoretical by the use of nitrogen gas as thepressure medium with a compacting pressure of about 13,000 psi.Examination of the as-compacted product indicated that it. was fullydense, e.g., a density approaching 100 percent of theoretical densityand homogeneous throughout. Also, a uniform metallurgical bond existedbetween the compacted powder and the core. The as compacted product wassuccessfully forged to a 5 in. billet and rolled into 2 in. bar stock;upon examination it was found that the metallurgical bond remainedintact during the forging and rolling operations. The ascompactedmaterial was capable of heat treatment to achieve a hardness of about 65R for the REX M7 material and 37 R with respect to the CSM 2 material.

EXAMPLE ll An additional trial was conducted similar to that reportedabove with respect to Example 1 except that the core was the MAXEL 3%composition reported in Table l and the powder was the REX M25 HCcomposition reported in Table I; the response to heat treatment of theans-compacted product was 66 R for the REX MZS HC material and 25 R. forthe MAXEL 3% material.

We claim:

1. A method for producing a composite alloy article comprising a lowalloy steel corc surrounded by compactcd high speed steel powder. saidmethod comprising surrounding a low alloy steel core with high speedsteel powder to form an assembly, hot isostatically compacting saidassembly at a temperature and pressure sufficient to compact said powderto a density greater than percent of theoretical and metallurgicallybond the same to said core, said pressure being at least 10,000 psi andsaid temperature being at least 2,000F. and upon completion of saidcompacting removing at least a portion of said core.

2. The method of claim 1 wherein said alloy core is fully dense prior tosaid compacting.

3. The method of claim 2 wherein said assembly is mechanically workedafter said compacting.

4. The method of claim 2 wherein said assembly after compacting issubstantially cylindrical and said core extends axially therein.

5. The method of claim 4 wherein an axial drilling is made through saidassembly at said core.

6. The method of claim 2 wherein said core and said powder are placed ina container for heating and compacting and subsequently removing saidcontainer from the compacted composite article.

7. A method for producing a composite alloy article comprising alow-alloy steel core surrounded by compacted high-speed steel powder,said method compris ing producing an assembly by placing a low-alloysteel core axially within a container and placing high-speed steelpowder in said container so that said powder surrounds said core, thensealing said container, isostatically compacting said assembly at atemperature and pressure sufficient to compact said powder to a densitygreater than 95 percent of theoretical and metallurgically bond the sameto said core, said pressure being within the range of 10,000 to 20,000psi and said temperature being within the range of 1,700 to 2,200F, andupon completion of said compacting removing said container and at leasta portion of said core.

8. The method of claim 7 wherein said compacted assembly is drilled toprovide an axial bore through said assembly at said core.

9. The method of claim 8 wherein said assembly is cyiindrical.

* i a a m

2. The method of claim 1 wherein said alloy core is fully dense prior tosaid compacting.
 3. The method of claim 2 wherein said assembly ismechanically worked after said compacting.
 4. The method of claim 2wherein said assembly after compacting is substantially cylindrical andsaid core extends axially therein.
 5. The method of claim 4 wherein anaxial drilling is made through said assembly at said core.
 6. The methodof claim 2 wherein said core and said powder are placed in a containerfor heating and compacting and subsequently removing said container fromthe compacted composite article.
 7. A method for producing a compositealloy article comprising a low-alloy steel core surrounded by compactedhigh-speed steel powder, said method comprising producing an assembly byplacing a low-alloy steel core axially within a container and placinghigh-speed steel powder in said container so that said powder surroundssaid core, then sealing said container, isostatically compacting saidassembly at a temperature and pressure sufficient to compact said powderto a density greater than 95 percent of theoretical and metallurgicallybond the same to said core, said pressure being within the range of10,000 to 20,000 psi and said temperature being within the range of1,700* to 2,200*F, and upon completion of said compacting removing saidcontainer and at least a portion of said core.
 8. The method of claim 7wherein said compacted assembly is drilled to provide an axial borethrough said assembly at said core.
 9. The method of claim 8 whereinsaid assembly is cylindrical.